The invention relates generally to systems for optically scanning a scene and generating electrical signals suitable for operating a television-type display. The invention relates particularly to systems where the optical scanning of one field of the scene is done in parallel, simultaneously using one photosensor for every line of the scene, rather than using one photosensor in zig-zag, scan-retrace raster-scanning fashion. Parallel scanning is useful in thermal imaging systems where the response time of a thermal sensor is inadequate for raster scanning. The parallel image line signals need to be stored, and then read out serially for application to a raster-scan television-type display. Since the elemental line scan video signals are analog signals each having any one of many values, the storage of the multi-level signals in the past has been difficult to implement. It is therefore desirable to provide an improved parallel-to-serial converter system in which advantage is taken of the analog signal handling capabilities of charge coupled devices. Such capabilities are described in U.S. Pat. No. 3,758,794 issued on Sept. 11, 1973, to W. F. Kosonocky for a "Charge Coupled Shift Register" and assigned to the assignee of this present application. Additional information is provided by the article "The New Concept for Memory and Imaging: Charge Coupling" by Lawrence Altman appearing in the June 21, 1971, issue of Electronics Magazine, pp. 50-59.